A photovoltaic cell converts radiant energy, such as sunlight, into electrical energy. In practice, multiple photovoltaic cells are electrically connected together in series or in parallel and are protected within a photovoltaic module or solar module.
A photovoltaic module typically comprises, in order, a light-transmitting substrate or front sheet, an encapsulant layer, an active photovoltaic cell layer, another encapsulant layer and a back-sheet. The light-transmitting substrate is typically glass or a durable light-transmitting polymer film. The encapsulant layers adhere the photovoltaic cell layer to the front and back sheets, they seal and protect the photovoltaic cells from moisture and air, and they protect the photovoltaic cells against physical damage and chemical attack. The encapsulant layers are typically comprised of a thermoplastic or thermosetting resin such as ethylene-vinyl acetate copolymer (EVA). The photovoltaic cell layer is any type of photovoltaic cell that converts sunlight to electric current such as single crystal silicon solar cells, polycrystalline silicon solar cells, microcrystal silicon solar cells, amorphous silicon-based solar cells, copper indium (gallium) diselenide solar cells, cadmium telluride solar cells, compound semiconductor solar cells, dye sensitized solar cells, and the like. The back-sheet provides structural support for the module, it electrically insulates the module, and it helps to protect the solar cells, module wiring and other components against the elements, including heat, water vapor, oxygen and UV radiation. The module layers need to remain intact and adhered to each other for the service life of the photovoltaic module, which may extend for multiple decades.
Photovoltaic cells have had electrical contacts on both the front and back sides of the photovoltaic cells. However, contacts on the front sunlight receiving side of the photovoltaic cells can cause up to a 10% shading loss. In back contact photovoltaic cells, all of the electrical contacts are moved to the back side of the photovoltaic cell. With both the positive and negative polarity electrical contacts on the back side of the photovoltaic cells, electrical circuitry is needed to provide electrical connections to the positive and negative polarity electrical contacts on the back of the photovoltaic cells.
In a back contact photovoltaic module, an integrated back-sheet having patterned electrical circuitry is electrically connected to back contacts on the photovoltaic cells during lamination of the solar module. A back-sheet 10 is shown in FIG. 1a with a metal foil adhered to a surface of the back-sheet substrate 14. The metal foil, such as a copper or aluminum foil, is patterned by etching, die cutting or other processes to form one or more electrically conductive circuits 12a, 12b, 12c and 12d. As shown in FIG. 1b, an interlayer dielectric (ILD) layer 16 is formed over the foil circuits, typically by laminating or screen printing a polymeric material over the electrically conductive circuit. Openings 18 are formed in the ILD where back electrical contacts on the photovoltaic cells are to contact the foil circuits. A thermoplastic or thermosetting encapsulant sheet 20 shown in FIG. 1c, typically an EVA sheet, is placed over the ILD layer with openings formed or punched out at locations corresponding to the openings in the ILD. An electrically conductive adhesive is applied in the openings of the ILD and encapsulant layers. Back contact photovoltaic cells 22a, 22b and 22c are placed on the encapsulant layer using pick and place technology, as shown in outline form in FIG. 1d with the position of the positive and negative polarity contacts on the back side of the solar cells shown. The back contacts on the photovoltaic cells align with electrically conductive adhesive inserted in the openings in the ILD and encapsulant sheet. The back contacts on the photovoltaic cell are adhered to and electrically connected to the metal circuits on the back-sheet by the electrically conductive adhesive by heating the electrically conductive adhesive, as for example in a thermal press. The positive polarity contacts of one solar cell are electrically connected in series to the negative contacts of an adjacent solar cell by the metal circuits, as shown in FIG. 1d. 
Aligning the openings of the ILD and/or encapsulant layers with electrically conductive circuits, inserting the electrically conductive adhesive into the aligned openings, and then aligning the back contacts of the back-contact solar cells with the openings in the encapsulant and ILD layers has been difficult to accomplish due to stretch, expansion, contraction and other flexibility in the encapsulant and/or ILD layers. There is a need for integrated back-sheet and encapsulant assemblies for back-contact photovoltaic modules in which the openings in the encapsulant and/or ILD layers are more easily and dependably aligned with the electrically conductive circuit of the integrated back-sheet and with the electrical contacts on the back of the back-contact solar cells.